The purpose of this research is to develop a technique of mass spectrometric analysis for thermolabile biomedical compounds. The technique under investigation has been called by several names, including direct source insertion, direct exposure, and surface chemical ionization. We have found the isopentane CI spectra of several thermolabile biomedical compounds to be very sensitive to the position of the sample in the source, the temperature of the sample, and the surface from which the sample is vaporized. These spectra are not strongly dependent on the incident electron energy, electron current or small variations in ionic translational energy. A separately heatable glass direct insertion probe has been developed. Studies will be made of the effects of rate of heating as well as final temperature on spectra. Comparisons will be made of spectra of easily dehydrated compounds vaporized from acidic, basic, and neutral matrices. Reagent gases such as isobutane, pyridine, and benzene will be used in comparison with isopentane on the relative abundances of (M plus H) ion or M ion ions. Indications of wall catalyzed decomposition reactions will be studied by comparing spectra in stainless steel, Teflon, and Vespel lined sources. Other probe designs and source configurations will be tried.